1. Field of the Invention
The present invention relates to a dynamic electric machine of the type having a guide plate which is disposed in a yoke and which guides tie bolts extending through the yoke in the axial direction. More particularly, the present invention is concerned with a structure for locating permanent magnets in this type of dynamic electric machine.
2. Description of the Related Art
In general, a dynamic electric machine of the type described requires that the permanent magnets to be mounted on the inner peripheral surface of a yoke have to be precisely located in order to attain a high degree of rotational precision of the machine. In order to precisely locate the permanent magnets, it has been a common measure to provide locating projections on the inner peripheral surface of the yoke. Each permanent magnet, when mounted, is placed such that its corner contacts the projection 10 so as to be precisely located on the yoke, as shown in FIG. 5A. In recent years, however, it has become popular to provide such permanent magnets 4 with corners which are rounded to avoid stress concentration, in order to prevent breakage or damage. When such a permanent magnet 4 having rounded corners is to be mounted in a yoke having a locating projection 10, the permanent magnet 4 tends to undesirably move onto the locating projection 10 as shown in FIG. 5B. This not only impedes the locating precision, but also causes a serious problem. Namely, when the machine is assembled while leaving the permanent magnet at a wrong position as shown in FIG. 5B, the permanent magnet 4 may dangerously interfere with the rotor during operation of the machine, thus impairing the quality of the product significantly.
The known magnet locating structure also suffers from a problem in that the yoke 2, which is formed by, for example, drawing, is undesirably deformed during a subsequent working for forming the locating projections 10. In addition, the outer surface of the yoke tends to become rusty due to accumulation of water in recesses 11 which are formed in the outer surface of the yoke as a result of the plastic work for forming the projections.
The permanent magnets located in the yoke are generally bonded to the yoke by means of, for example, an epoxy-type adhesive. The bonding is usually conducted while the yoke is held with its axis extending vertically. It has been often experienced that the adhesive, which has become less viscous due to heat, undesirably flows down to clog draining holes formed in the peripheral wall of the yoke or bolt holes provided in the bottom of the yoke, and even flows into the portion of the yoke in which a bearing is to be fitted.